WASHINGTON/MEXICO CITY (Reuters) - The head of Russian oil company Rosneft (ROSN.MM), Igor Sechin, flew to Caracas this week to meet Venezuelan President Nicolas Maduro and complain over delayed oil shipments designed to repay loans, two sources briefed on the conversation said on Saturday.

FILE PHOTO: Rosneft Chief Executive Igor Sechin attends the talks of Russian President Vladimir Putin with South Korean President Moon Jae-in at the Kremlin in Moscow, Russia June 22, 2018. REUTERS/Sergei Karpukhin/File Photo

The visit, which was not publicly disclosed, is one of the clearest signs of strain between crisis-stricken Venezuela and its key financier Russia.

Over the last few years, Moscow has become Venezuela’s lender of last resort, with the Russian government and Rosneft handing Venezuela at least $17 billion in loans and credit lines since 2006, according to Reuters calculations.

State oil company PDVSA is repaying almost all of those debts with oil, but a meltdown in its oil industry has left it struggling to fulfill obligations.

Sechin and a large delegation of executives met with officials at PDVSA in a Caracas hotel this week. Sechin also met with Venezuela’s leftist leader Maduro, and chided him overoil-for-loans shipments that are behind schedule.

“He brought information showing that they were meeting obligations with China but not with them,” said one source with knowledge of the talks.

“They’re running around in PDVSA because of this,” added the source, asking to remain anonymous because he was not authorized to speak to media.

The country’s oil production has fallen to just 1.17 million barrels-per-day, a 37 percent drop in the last year, according to reports from secondary sources to OPEC, leaving itstruggling to ship Russian entities the roughly 380,000 bpd it has agreed to send, according to PDVSA documents seen by Reuters.

The closing of a dock at Venezuela’s main oil export port, through which the vast majority of shipments to Rosneft transit, has delayed millions of barrels in crude since August.

Top financier China, which has ploughed more than $50 billion into Venezuela, also gets reimbursed in oil.

According to Reuters calculations based on PDVSA data, the Caracas-based company delivered around 463,500 bpd to Chinese firms between January and August, a roughly 60 percent compliance rate. That compares with around 176,680 bpd to Russian entities, or a 40 percent compliance rate.

Rosneft and PDVSA did not immediately respond to a request for comment.

One of the sources with knowledge of Sechin’s visit, as well as two separate sources, said a Chinese delegation was also in Caracas this week.

CHINA, RUSSIA VIE FOR VENEZUELA OIL

As of early 2017, PDVSA began to fall months behind on shipments of crude and fuel under the loan deals with China and Russia due to problems in its oil industry, home to the world’s biggest crude reserves, according to documents reviewed by Reuters.

The problems include operational mishaps, such as refining outages and delayed cleaning of tanker hulls, and financial disputes with service providers owed money by PDVSA.

This April, Rosneft and PDVSA signed a refinancing agreement designed to allow the Venezuelan company to catch up on delayed loan payments by delivering more crude to Rosneft. Under the refinancing, PDVSA has to provide Rosneft with some 380,000 bpd, up from around 310,000 bpd, according to Reuters calculations.

The Russian company was planning on using Jose’s South dock to pick up the cargoes, before an August tanker collision delayed exports to Rosneft. PDVSA reopened the dock earlier this month, sources said.

China agreed to use ship-to-ship (STS) operations to avoid Venezuela’s clogged ports. However, the clients to whom Rosneft sends Venezuelan crude, Russian-backed Indian refiner Nayara Energy and Indian conglomerate Reliance, did not agree to STS transfers, likely heightening delays.